Prior Art FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, a pair of bases 102 is equipped with row bars 104 each including a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the row bars 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in communication with the readers and writers 106. More information regarding such flat-lapped magnetic tape head may be found with reference to U.S. Pat. No. 5,905,613, which is incorporated herein by reference.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angle 110 defined between a horizontal plane and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angle 110 includes an internal wrap angle which is often similar in degree to an external wrap angle 115. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. Such parameters are adjusted to deal with various operational aspects of heads such as that of Prior Art FIG. 1, in a manner that will soon become apparent.
During use of the head of FIG. 1, various effects traditionally occur. Prior Art FIG. 2A is an enlarged view of the area encircled in FIG. 1 that illustrates a first known effect associated with the use of the head 100 of FIG. 1. As shown, tents 202 form in the tape 108 on opposite edges of the tape bearing surface 109.
Prior Art FIG. 2B is a cross-sectional view of the head 100 of FIG. 1 taken along the illustrated line of FIG. 2A. As shown, tape lifting 204 occurs along side edges of the tape bearing surface 109 as a result of air leaking in at the edges and tape mechanical effects. Lifting adversely affects the end portions of the readers and writers 106. Still yet, the tape lifting 204 results in additional stress at points 206 which, in turn, causes additional wear. Further augmenting such tape lifting 204 is the fact that the tape 108 naturally has upturned edges due to widespread use of technology applied in the video tape arts.
During the design of tape heads like that of FIG. 1, the tape bearing surface length 112 and tape wrap angle 110 may be varied to minimize the impact of some of the foregoing effects. For example, it is desirable that the tape bearing surface length 112 be elongated in order to reduce interaction of the aforementioned tents 202, which may, in turn, significantly reduce the proper communication between the tape 108 and the readers and writers 106. Moreover, wear of the edges of the tape bearing surface 109 may result in shortening of the tape bearing surface length 112 over time. Thus, if the tape bearing surface length 112 is, at one time, sufficient to reduce the foregoing interaction, the shortening of the tape bearing surface length 112 may prompt such interaction over time. On the other hand, it is also desirable that the tape bearing surface length 112 be shortened to reduce the aforementioned lifting at the tape edges set forth during reference to FIG. 2B.
With respect to the tape wrap angle 110, there is a desire to increase such angle to combat the “edge loss” affect associated with the tape lifting 204 of FIG. 2B. On the other hand, there is a desire to minimize such tape wrap angle 110 to minimize the lateral extent (length in the direction of the tape motion) of the tents 202 of FIG. 2A.
The balancing of the foregoing aspects has resulted in the design of tape heads 100 with a tape bearing surface length 112 of approximately 0.8 mm, and a tape wrap angle 110 of approximately 1.8 degrees.
Recently, studies have shown that high frequency output of traditional flat-lapped bi-directional, two-module magnetic tape heads, with certain tapes, can vary with tape speed. In particular, increasing tape speed of those tapes causes an increase in fly height, and thus a decrease in high frequency output. Still yet, this effect is lessened with continued use of that particular tape sample. FIG. 2C illustrates such a relationship between the resolution (i.e. ratio of high frequency to low frequency output) of the tape head 100 and a velocity of the tape 108. While this effect is obscured to a small extent with many media, it is particularly pronounced for other media.
Thus, as tape speed increases, resolution decreases because of this effect. Changes in resolution generally require changes in read equalization to keep error rates low, especially for partial response maximum likelihood (PRML) channels. This means that in applications requiring “speed matching” in which drive speed varies in response to user-attached system speed, error rates may change with tape speed. It is a common goal that error rates be maintained at lowest possible levels under all operating conditions.
The origin of this effect (fly height or resolution vs. speed) is not fully understood. There has been a suggestion that it is related to viscoelastic stiffening of certain tapes as speed increases. There is thus a need for a head that addresses this problem of certain tapes, and gives a substantial improvement.
Fundamentally, the relationship shown in FIG. 2C appears to be a wrap angle-controlled effect. At larger tape wrap angles, the speed effect is more pronounced than at lower wrap angles with the affected tapes.
As mentioned earlier, tape “tents” form on each edge of a head. See FIG. 2A. The greater the wrap angle, the higher and longer the tent. Modeling and experiments have shown that at any tape speed larger tents tend to suck more air into the head-tape interface and thus results in an increase in head-tape separation in the region of the recording head.
For given geometrical wrap angles, stiffer tapes will have larger tents. If the tape appears dynamically stiffer as speed increases due to viscoelasticity, larger tents and a greater fly height may result. In any case, shallow wrap angles give lower and less speed dependent fly heights.
Most tapes are manufactured with “cupping,” which is the tendency for the tape surface to be convex when viewed from the magnetic coating side. This property, which is needed for helical scan applications to prevent the heads from knicking the tape edges, coupled with anticlastic bending and side air leakage, tends to make the edges curl away from the flat head surfaces. This is particularly a concern when there are servo tracks near the edges of the tape, such as with Linear Tape Open (LTO) standard tapes. Increasing the tape wrap angle tends to “straighten” the wrapping and generally reduce edge lifting, but this has the negative effect already described hereinabove.